Low density polyethylene (LDPE) can be produced by high pressure polymerization in the presence of radical initiating agents. Two basic high pressure polymerization processes for the manufacture of LDPE are autoclave and tubular.
The autoclave reactor process can produce LDPE (“autoclave LDPE”) having a high concentration of long chain branches and a relatively broad molecular weight distribution. It is believed that the high concentration of long chain branches results in high values of elongational hardening while the broad molecular weight distribution renders the polymer easy to process.
Unfortunately, the autoclave process can be carried out in the presence of organic peroxides as the radical initiating agents. The organoleptic properties such as odor of LDPE are harmed in the presence of the degradation products of organic peroxides.
The tubular reactor process can produce LDPE (“tubular LDPE”) having better organoleptic properties because the tubular process does not require the use of organic peroxides. As such, the tubular process avoids producing the degradation products of organic peroxides. (The tubular process can be carried out by using oxygen alone as the radical initiating agent.)
Unfortunately, the tubular LDPE has a lower concentration of long chain branches and a narrower molecular weight distribution than the corresponding autoclave LDPE. The tubular LDPE is less useful for applications requiring high processability, such as extrusion coating.
There is a need to obtain a LDPE product having high elongational hardening and broad molecular weight distribution, without using organic peroxides.
There is also a need to maintain the density of the LDPE product.